Monitoring El Giraldillo in Seville

El Giraldillo is a 5 meter high bronze sculpture weighing 2000 kilos, which crowns the top of the tower of La Giralda, the Seville Cathedral. This 98 meter high tower is a former Almohaden minaret and at the time of its erection in 1184, was the highest tower in the world. As well as its decorative function, since 1568, El Giraldillo has also served as a weather vane from the highest point of the town.

Between 1999 and 2005, a monitoring system was fitted to El Giraldillo to detect any potential deterioration in the structure enabling timely restoration work to be undertaken.

The specialist construction group of the Escuela Superior de Ingenieros de Sevilla (University of Engineering) decided to use the MGCplus amplifier system to monitor any mechanical changes to the sculpture.

Working together with HBM, different sensors were installed to record the most important mechanical states connected with the mechanical behavior of the sculpture (movement, mechanical stress, bending moment, torque, acceleration). Installed above the weather vane support were three strain gage full bridges to measure bending moment and torque, accelerometers to analyze the movements of the structure and inclinometers to detect the long-term tendencies of the mast to tilt.

Fig. 1: Measuring chain for remote monitoring of El Giraldillo. Data are transmitted to the University of Seville via the WiFi™ network

The wind speed, wind direction, temperature and atmospheric humidity were also measured, in order to relate the external conditions to the principal mechanical measurements. Corrosion sensors were also installed to detect possible chemical reactions at the junction points of different metals.

All measurement signals are evaluated by an MGCplus amplifier and stored on a CP42 hard disk, which can then be called up by the university via a 2.8-km WiFi link.

The basis for the success of this project is our close collaboration with our partner, HBM Ibérica, who helped enormously in setting up the sensors, cabling and measurement system.